HEAT RETENTION (also called heat stroke, or heat pyrexia) arises from a disturbance of the normal balance between heat gain to the body and heat loss. The principal factors concerned with heat balance are shown in Figure 1.
Of the four physical processes by which heat loss is mediated, evaporation is the most important in hot environments. When air temperature becomes equal to skin temperature (about 94 F. dry-bulb temperature), radiation and convection are no longer avenues of heat loss, and cooling is effected solely by evaporation. It can be seen from the Table that above a room temperature of 85 F., the temperature in the patient's immediate environment, i. e., under the drapes, is 96 F. or more. Hence, above this room temperature it is clear that in any patient in whom the sweating mechanism fails heat retention will almost certainly develop.
The signs of heat retention occurring in